Biology 100/101
Fall 1997
Lecture 22:
Microevolution: Allele Frequencies

Text Readings
in Lewis		 Review questions
Chapter 18
Chapter 20		 Pg. 388: To Review;
1, 2, 3, 5, 6, 7, 9, and 10
To Think About; 4 and 7
Pg. 420-1: To Review;
1, 3, 5, 6, and 7
To Think About; 3, 6 and 7

For feedback, post possible answers and ideas in the folder "Text 'Review' and 'To Think About' Questions" in the Biology Chat Section of Web Crossing.

Objectives
 After studying this material you should be able to:

  1. describe biological evolution in terms of change in allele frequency in a population.

  2. list and explain Darwin's main ideas concerning natural selection and evolution.

  3. explain why survival is necessary, but insufficient as a criterion for judging the adaptiveness of a trait.

  4. describe evolution as changes in allele frequency resulting from directional, stabelizing, and disruptive selection.

  5. provide examples of evolution resulting from natural selection.

  6. describe an example in which natural selection has affected the virulence and/or spread of a human disease.

Key Terms:
Understand the relationships among these terms:

biological evolutionselectionnatural selection
microevolutionmutationallele frequencies
directional selectionstabilizing selectiondisruptive selection
genetic variationscientific theoryscientific fact
differential reproductionsexual selection"fitness"
macroevolutionbalanced polymorphism

Web Resources for Evolution

  • The Talk.Origins Archive - a compilation of information and conversations about evolution. Includes a search option.

  • Biology and Evolutionary Theory This is a menu page from Talk.Origins with links to essays about evolution including some of those below and others you might find interesting.

  • Introduction to Evolutionary Biology Version 2 (from Talk.Origins)
    This is rather lengthy, but scan through it to help with the terms in the table above.

  • What is Evolution?

  • Evolution is a Fact and a Theory

  • The basics of sexual selection

  • Sexual selection 2

  • Discovery Chanel Online: Beyound Darwin, by Bill Belleville

  • Creationism - (with an obvious Evolutionist spin from Talk.Origins)

  • Charles Darwin Research Station Galapagos Islands

  • Other Links from Talk.Origins
    This includes links to creationist pages as well as others.

    Web Crossing Resources

    Extra Credit Discussion - Book Reviews of The Beak of the Finch, Origins Reconsidered, and The Diversity of Life

    Some of your classmates are reading, reviewing, and discussing these three books dealing with natural selection and evolution.

    For Starters: BUGHUNT! - A computer model of natural selection.

    Darwin's Main Ideas, pg. 383, Lewis
      Facts Based on Observations of Nature:

    1. Organisms are varied, and some variations are inherited. Within a species, no two individuals (except identical siblings) are exactly alike.

    2. More individuals are born than survive to reproduce

    3. Individuals compete with one another for the resources that enable them to survive

      Inferences from Observations:

    4. Within populations, the characteristics of some individuals male them more able to survive and reproduce in the face of certain environmental conditions..

    5. As a result of the environment's selection against nonadaptive traits, or "survival of the fittest", only individuals with adaptive traits live long enough to transmit traits beneficial in that environment. Over time, natural selection can change the characteristics of populations, even molding new species.

    Another "Take" on Darwin's thinking from Ernst Mayr -
    a distilation of Darwin's ideas into 5 theories:
    *What is Darwinism? (Talk.Origins)

    1. Evolution as such. This is the theory that the world is not constant or recently created nor perpetually cycling, but rather is steadily changing, and that organisms are transformed in time.

    2. Common descent. This is the theory that every group of organisms descended from a common ancestor, and that all groups of organisms, including animals, plants, and microorganisms, ultimately go back to a single origin of life on earth.

    3. Multiplication of species. This theory explains the origin of the enormous organic diversity. It postulates that species multiply, either by splitting into daughter species or by "budding", that is, by the establishment of geographically isloated founder populations that evolve into new species.

    4. Gradualism. According to this theory, evolutionary change takes place through the gradual change of populations and not by the sudden (saltational) production of new individuals that represent a new type.

    5. Natural selection. According to this theory, evolutionary change comes about throught the abundant production of genetic variation in every generation. The relatively few individuals who survive, owing to a particularly well-adapted combination of inheritable characters, give rise to the next generation.

    Survival is necessary, but insufficient as a criterion for judging the adaptiveness of a trait. What is the measure of "fitness"? (Sexual Selection)

    *Evolution is a Fact and a Theory

    Natural Selection is One of Several Mechanisms of Microevolution

    Types of Natural Selection

    Evolution and disease ("New" Diseases, Mutation, and Evolution of Resistance)